1. Field of the Invention
The present invention relates to the identification of an electronic component or assembly based on parameters linked to the manufacturing of an identification circuit contained in an integrated circuit chip. Such an identification generally uses a network of physical parameters (PPN) linked to the manufacturing of the integrated circuit chip. This identification is currently designated as an “integrated circuit fingerprint” identification.
2. Discussion of the Related Art
A first family of known identification methods consists of measuring electric parameters of the integrated circuit chip. It may be, for example, a measurement of a threshold voltage of a transistor, a resistance measurement or a stray capacitance measurement. Since these features are sensitive to technological and manufacturing process dispersions, it can be considered that the electric parameter(s) taken into account are specific to a manufacturing and form a “signature” of the integrated circuit resulting from this manufacturing. An example of a method using a measurement of electric parameters is described in U.S. Pat. No. 6,161,213 which is incorporated herein by reference.
A disadvantage of the use of an electric parameter measurement is that these values vary along time (during the circuit lifetime). Accordingly, the obtained signature is not stable.
Another disadvantage is that it is necessary to calculate the difference between a measured signature (for example, the voltage across a capacitor) and a predefined signature. It is accordingly necessary to have an analog-to-digital converter to convert the measured signals before calculating their difference enabling identification.
In addition to stability problems, the converter needs to be very accurate due to the small variations to be measured. Indeed, the technological dispersions involved are, by nature, very small (for example, for the threshold voltage of a MOS transistor, the dispersion generally is +/−4 millivolts. For a voltage measurement, a difference smaller than one millivolt over a range of values of approximately 200 millivolts may have to be detected. For such an example, a 12-bit converter is necessary.
Another disadvantage is that, for reliability reasons, it is often necessary to examine several points in the circuit. This accordingly requires an analog multiplexer, or increasing the number of used converters.
A second family of known solutions uses a time measurement. For example, the read/write time of an EEPROM-type memory is measured. An example of an identification method using an operation execution time measurement is described in U.S. Pat. No. 5,818,738which is incorporated herein by reference.
This family of solutions has the same disadvantages as the former. The difference is that the converter is replaced with a counter.
Be it in the first or in the second solution family, a measurement is used and the obtained signature is compared with a standard value stored either in the integrated circuit or in an external device in the case of an authentication with respect to distant elements.
All these solutions thus have the major disadvantage of being bulky and difficult to implement for an uncertain result.